1. Field of the Invention
The present invention relates to an apron feeder for use in the bulk materials industry and, more particularly, an apron feeder incorporating an integral weighing device.
2. Description of the Prior Art
Apron feeders are typically used in the mining, cement, and other bulk materials industries for extracting bulk materials from bins, hoppers, silos, stockpiles, and the like. The apron feeders are then used to transfer the material to another location. Some specific uses of apron feeders known in the art are applications such as feeding and withdrawing materials from primary crushers, loading and unloading trucks and railcars, removing frozen materials from storage, feeding jaw crushers and belt conveyors, and high abrasion applications frequently found in reclaim circuits. Two examples of apron conveyors known in the art are found in U.S. Pat. Nos. 3,934,712 to Jende and 1,537,444 to Herzog, the disclosures are incorporated herein by reference.
Apron feeders, particularly xe2x80x9ctractor typexe2x80x9d apron feeders, are often confused with other types of feeders such as pan or belt feeders. Those skilled in the art will appreciate that apron feeders are distinguishable from pan or belt feeders because pan and belt feeders are not capable of being used in the heavy, bulk materials industry such as mining. Apron feeders are uniquely suited for feeding large, lumpy, abrasive, and heavy materials. Pan or belt feeders are not suitable for use with such materials and are typically limited to light duty operations only. Thus, apron feeders are considered in the art to be distinguishable from pan or belt feeders.
Apron feeders come in many different configurations. However, apron feeders generally share certain characteristics in common. Typically, apron feeders include a feeder frame upon which a drive roller is rotatably mounted. A tail roller is located at an opposite end of the feeder frame from the drive roller. A plurality of idler rollers is located between the drive roller and tail roller. Apron feeders further typically include a series of interconnected metal pans or flights that are reeved about the drive roller and tail roller and supported by the idler rollers between the drive roller and tail roller. Two or three strands of endless conveyor chain are often used to drive the pans and material carried thereon.
One known configuration for apron feeders locates the endless conveyor chain outboard of the flights such that the conveyor chain does not directly support the weight of the material on the flights. This arrangement is known as an outboard chain design. Another configuration known in the art for apron feeders was introduced in the early 1970""s and is known as a xe2x80x9ctractor typexe2x80x9d apron feeder. A tractor type apron feeder utilizes tractor type undercarriage chain and rollers that are used on bulldozers and excavators. In the tractor type configuration, one or more conveyor chains are located under the flights. In recent years, tractor type apron feeders, also referred to as crawler apron feeders, have become the preferred design for use in the heavy materials industry.
It is well-known in the art to include a load cell assembly or weighing system with belt conveyors. For example, U.S. Pat. Nos. 4,463,816 to McFarlane; 3,478,830 to Levesque et al.; and 2,882,036 to Lyons are generally directed to belt conveyor weighing systems in which a load cell is located below the belt conveyor for weighing the material received on the surface of the belt conveyor. Specific belt scales for weighing material moving on a belt conveyor supported by an idler assembly are known from U.S. Pat. Nos. 5,294,756 to Lauber et al. and 5,285,019 to Kempf et al. The belt conveyor scale arrangements known from Lauber et al. and Kempf et al. generally disclose the use of a load scale located below an idler support of the belt conveyor. A typical weighing arrangement 10 for a belt conveyor is shown in FIG. 1. The disclosures of each of the foregoing listed patents are incorporated herein by reference.
In FIG. 1, the contents of a hopper or bin 12 may be extracted to an apron feeder 14 located below the hopper 12. To perform a weighing operation, the apron feeder 14 delivers material to a belt conveyor 16 that includes a belt conveyor scale 18. The belt conveyor 16, after weighing the material, delivers the material to a downstream product conveyor 20 through a crusher 22 or other piece of equipment. The arrangement shown in FIG. 1 is well-known in the heavy materials industry. The apron feeder 14 is provided primarily to absorb the heavy weights associated with the extraction of bulk materials from the hopper 12. The weighing step is performed entirely by the belt conveyor 16.
U.S. Pat. No. 4,823,440 to Pinto is directed to a web weight control system for weighing fibers supplied to a carding machine that incorporates an apron conveyor. The apron conveyor includes a weighing device defined by a plunger and a horizontal rod, which bears against the underneath portion of the upper run of the apron conveyor. A transducer is used for sensing the load on the apron conveyor and then sends a weight control signal to a computer. As will be appreciated by those skilled in the art, Pinto discloses the use of an apron conveyor for light, loose fabrics and is not believed to be pertinent to the apron weigh feeder of the present invention, which is specifically directed for use with heavy bulk materials and is a tractor type apron feeder.
In view of the foregoing, an object of the present invention is to provide an apron feeder capable of extracting and weighing heavy bulk materials at the same time with one piece of equipment.
The above object is accomplished with an apron weigh feeder in accordance with the present invention. The apron weigh feeder of the present invention is intended for use in the heavy, bulk materials industries, such as the mining and cement industries, to extract various types of materials from beneath hoppers, storage bins, silos, reclaim piles, and the like. The apron weigh feeder is a tractor type, also referred to as a crawler type, apron feeder and is capable of weighing extracted material as the material is conveyed from an extraction end to a discharge end of the apron weigh feeder. The apron weigh feeder simultaneously transports and weighs heavy bulk materials.
In general, the apron weigh feeder of the present invention includes a feeder frame, a head drive shaft, a tail traction wheel, a plurality of carry rollers, an endless crawler chain, a plurality of flights, and a weigh scale assembly. The head drive shaft is mounted rotatatably on the feeder frame. The head drive shaft has a drive sprocket mounted thereto. The tail traction wheel is mounted rotatably on the feeder frame at an opposite end of the feeder frame from the head drive shaft. The tail traction wheel is aligned with the drive sprocket. The carry rollers are located and aligned between the drive sprocket and tail traction wheel. The carry rollers are supported rotatably by a plurality of carry roller support frames, respectively. The carry roller support frames are each mounted on the feeder frame. The crawler chain is reeved about the drive sprocket and tail traction wheel. The crawler chain in operation of the feeder moves in a chain path comprised of an upper rectilinear path and a lower rectilinear path connected by two curvilinear paths. The crawler chain is supported by the carry rollers while moving in the upper rectilinear path. The flights are fixed to the crawler chain to define a carrying surface of the feeder. The weigh scale assembly is substituted in place of at least one of the carry roller support frames. The weigh scale assembly is operable to generate an output signal indicative of the weight of bulk material passing over the weigh scale assembly.
The weigh scale assembly may comprise a scale support frame substituted in place of the at least one carry roller support frame and a load cell positioned between the scale support frame and the feeder frame. The load cell is configured to generate the output signal indicative of the weight of bulk material passing over the scale support frame and load cell. The load cell may be operatively connected to a feeder scale configured to display the output signal as the weight of bulk material. The weigh scale assembly may comprise a pair of load cells positioned between the scale support frame and the feeder frame and located on opposite longitudinal sides of the feeder. The scale support frame may support at least two adjacent carry rollers.
The apron weigh feeder may further include a plurality of return rollers mounted rotatably on the feeder frame below the carry rollers. The return rollers are preferably fewer in number than the carry rollers. The sidewalls of the flights may be supported by the return rollers as the crawler chain moves along the lower rectilinear path.
The apron weigh feeder may further include a speed sensor connected to the head drive shaft. The speed sensor is configured to generate an output signal indicative of the rotational speed of the head drive shaft. Control means may be operatively connected to the weigh scale assembly and speed sensor for receiving the output signals from the weight scale assembly and speed sensor. The control means may be configured to calculate the mass flow rate of bulk material carried by the feeder based on the output signals.
The apron weigh feeder may have an extraction end for receiving bulk material onto the flights and a discharge end from which bulk material is discharged from the feeder. The weigh scale assembly is preferably located substantially at the discharge end of the apron weigh feeder.
The apron weigh feeder in accordance with the present invention may have two or more drive sprockets mounted on the head drive shaft and include two or more tail traction wheels aligned with the drive sprockets, respectively. The plurality of carry rollers may be arranged in substantially parallel rolls aligned between respective pairs of drive sprockets and tail traction wheels. An endless crawler chain is preferably reeved about each of the respective pairs of drive sprockets and tail traction wheels. The scale support frame may be configured to support at least two adjacent pairs of carry rollers. The flights may be configured to extend transversely across the multiple crawler chains.
Further details and advantages of the present invention will become apparent from the following detailed description, read in conjunction with the drawings.